The present investigation encompasses chemical synthesis and characterisation (UV-visible spectra (UV-Vis), X-ray diffraction (XRD), dynamic light scattering (DLS), field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM)) of cadmium sulphide nanoparticles (CdS-NPs; quantum dots, possessing unique photo-physicochemical properties) and its potentiality to induce heritable phenotypic changes in Macrotyloma uniflorum (Lam.) Verdc. (Leguminosae; annual herb with therapeutic and nutritional uses). Dry seeds (moisture content 11.41 %) are exposed (3.2, 6.4, 12.7 and 19.1 μg mL −1 , 24- and 48-h durations) to CdS-NPs (size: 1.2 to 2.2 nm; shape: cubic to spherical) and bulk CdS (3.2 μg mL −1 , 24 h). Dissolution potentiality measured in in vitro system (using dialysis bags) shows high diffusibility (73.5 % ± 2.04 to 77.2 % ± 3.01) from lower (3.2 μg mL −1 ) to higher (19.1 μg mL −1 ) concentrations suggesting its effective penetration in in vivo system (seeds) as well. Accumulation of CdS-NPs and bulk CdS in seedlings (Petri plate germinated) is also studied in the form of Cd 2+ by atomic absorption spectroscopy (AAS). CdS-NPs induce five phenotypic variants (two non-viable: ‘viridis’ and ‘glossy leaf’; three viable: ‘broad elongated leaf’, ‘bushy’ and ‘unbranched’) at M 2 . Selfed seeds of the variants segregated (either 3:1 or 1:1) at M 3 in accordance with Mendelian pattern confirming them to be macromutants. The phenotypic mutants show normal meiotic chromosome behaviour alike to control plants (2 n  = 20) but with lower pollen fertility. The mutants bred true at M 4 generation. ‘Broad elongated leaf’ and ‘bushy’ mutants are highly productive types (in relation to seed yield) in comparison to control plants. ‘Unbranched’ phenotype can be an important genetic resource for efficient breeding. CdS-NPs inducing heritable phenotypic changes open up the possibility of using them as an alternative source for conventional mutagens.